The field of invention relates to semiconductor process technology generally; and, more specifically, to mask inspection technology for semiconductor processing masks.
Masks are used in semiconductor processing to properly form regions of light that are subsequently directed onto a semiconductor substrate. Depending on the type of resist (e.g., positive or negative) that is coated upon the substrate, the regions of light formed by the mask correspond to either the specific structures formed on the surface of the semiconductor substrate (e.g., gate electrodes, source/drain electrodes, vias and interconnect lines, among others) or the spaces between these structures.
Masks are patterned in a manner that corresponds to the structures formed on the substrate. A mask essentially affects the optical path between an exposure light source and the semiconductor substrate. The patterns on the mask prevent various portions of the exposure light from reaching the semiconductor substrate. As such, the mask is often said to be patterned with opaque as well as non opaque regions.
During the design sequence of a semiconductor integrated circuit (IC), one or more netlists associated with the gate or transistor level design are converted into an IC layout that is consistent with the ground rules of the applicable semiconductor manufacturing process. A mask is usually created for each level of the semiconductor manufacturing process. Thus after successive iterations of a mask manufacturing sequence (for each semiconductor device level), a mask set is formed that is used for the manufacture of the overall IC. The process of FIG. 1 corresponds to the making of each individual mask within the mask set.
The design 101 of each mask is typically performed, within a software environment, as a combination of automated and manual efforts. Designing a mask involves determining various mask patterns that correspond to the desired semiconductor substrate features. The patterns on a particular mask are stored in a file upon completion of the design.
The file produced at the end of the mask design sequence, globally referred to as a xe2x80x9cmask design filexe2x80x9d or xe2x80x9cpolygon filexe2x80x9d or xe2x80x9cphysical image filexe2x80x9d is essentially a record of the patterns to be formed on the mask. The record typically appears as an arrangement of shapes (such as squares and rectangles) and is used as a blueprint for the mask manufacturing sequence. Currently, the file types used for mask design files include DRACULA, GDS, GDSII and Transcription Enterprise among others such as proprietary file types.
During mask manufacturing 102 a radiation source (such as an E beam writing apparatus) xe2x80x9cwritesxe2x80x9d or otherwise transfers the shapes associated with the mask design file onto the mask surface. The mask is eventually formed (by methods known in the art) such that the design file""s patterns correspond to opaque or non opaque regions. During manufacture of the semiconductor IC, as discussed above, opaque regions prevent light from reaching the semiconductor substrate and non opaque regions either transmit or reflect light to the semiconductor substrate.
After complete or partial manufacturing 102 of a mask, the quality of the patterns formed on the mask are checked or otherwise reviewed. This checking sequence is generally referred to as mask inspection 103 coupled with a comparison 104 of the manufactured mask with the mask design file. Mask inspection 103 usually involves placing the mask into an apparatus, referred to as a mask inspection tool, that sweeps a small spot of light upon the mask surface. Sweeping may be accomplished by moving the mask beneath a fixed beam; moving a beam across the fixed mask or moving both the beam and the mask. In other instances a line rather than a small focused spot is swept. Furthermore, as discussed in more detail ahead, mask inspection may be accomplished by a scanning spot approach or an imaging approach.
The signal from the mask inspection tool optical system that is observed at a particular mask coordinate is stored into an inspection measurement data file for each mask coordinate the spot is focused upon. For transmission masks, the signal corresponds to the amount of focused light that passes through the mask. For reflection masks the signal corresponds to the amount of focused light that reflects off of the mask.
By comparing these stored signals against the mask design file for each applicable mask coordinate, defects may be automatically detected. For example, if an area located at a particular mask coordinate is designed to be 100% opaque, there should not be any observed signal (negating system noise). The detection of non zero intensity could indicate the presence of undesired holes in the mask at this particular coordinate.
A problem with this automatic detection of errors, however, is the inherent accuracy associated with comparing raw design file data against the inspection measurement data file. Due to the inherent presence of acceptable differences between the mask design file and the inspection measurement data file, the automated mask checking sequence 103, 104 falsely identifies many xe2x80x9cdefectsxe2x80x9d in the manufactured mask that are, in fact, not actual defects.
A method is described comprising accepting a mask design file input and then simulating the inspection of a mask through an optical channel. The mask design file has patterns. The optical channel corresponds to a mask inspection tool optical channel. The mask is patterned according to the mask design file patterns.